1. Field of the Invention
The present invention relates to a drum brake seal structure for an all-terrain vehicle wheel, and more particularly to a drum brake designed to reliably provide a seal between a brake panel and a brake drum even when the brake drum is accidentally displaced from the brake panel.
2. Description of the Related Art
Drum brakes are well known in the art. FIG. 3 hereof shows in cross-section one example of such drum brakes. A drum brake 100 includes a brake panel 101, and a brake drum 105 rotationally mounted to an axle 103 by means of bearings 104, 104. The brake panel 101 has brake shoes 102, 102 (only one shown) operably attached thereto. The brake shoes 102, 102 are disposed to produce friction force in cooperation with the brake drum 105. On an end portion 111 of the brake drum 105, there is mounted a seal member 106. The seal member 106 has lips 107, 108 pressed against a surface of the brake panel 101. A wheel cylinder 112 is provided for pressing the brake shoes 102, 102 against an inner peripheral surface of the brake drum 105. A wheel 114 is attached to the brake drum 105 by means of a bolt 113 and a nut 115. Reference numerals 116, 117 denote an oil seal and a knuckle, respectively.
The end portion 111 of the brake drum 105 is normally spaced from the surface of the brake panel 101 by a distance L1, as shown in (a) of FIG. 4.
As an all-terrain vehicle employing the drum brake 100 travels, the axle 103 can be subjected to an external force.
If the axle 103 is undesirably bent by such an external force, the brake drum 105 may be displaced away from the brake panel 101, as shown by an arrow in (b) of FIG. 4, to thereby provide a distance L1+.alpha. between the brake drum 105 and the surface of the brake panel 101.
As the brake drum 105 is displaced away from the brake panel 101, the contact area of the lips 107, 108 and the brake panel 101 becomes less. Thus, when the brake drum 105 is greatly displaced away from the brake panel 101, as shown in (b) of FIG. 4, the seal member 106 can not reliably provide a seal between the brake drum 105 and the surface of the brake panel 101.